The purpose of this protocol is to develop a valid, reliable, better standardized, and more efficient test of visual acuity (ability to see fine details) for use in clinical trials. Recent improvements in computer video hardware permit calibration, characterization, and accurate rendering of eye-chart-quality letters. The computer can then be used to measure acuity. The modified binary search (MOBS) testing strategy is one method of computer-based testing. This study will compare the accuracy, precision, stability and utility of the MOBS technique with the eye chart method used in the National Eye Institute's Early Treatment for Diabetic Retinopathy Study (ETDRS). The ETDRS method is currently the gold standard for acuity testing in clinical trials.